The world requires ever-increasing amounts of fuel for vehicle propulsion. Means of utilizing fuels needs to be accomplished more efficiently and with substantially lower carbon dioxide emissions and other air pollutants such as NOxs.
The gas turbine or Brayton cycle power plant has demonstrated many attractive features which make it a candidate for advanced vehicular propulsion. However, the gas turbine does not allow the normal “engine braking” or “compression braking” feature that is extensively used in piston-type engines. Further, many modern regenerative braking systems rely on batteries or other electrical storage subsystems to receive and absorb excess braking energy (others utilize pneumatic or hydraulic storage). In most cases, the cost of this energy storage is significant. Sizing a typical battery or ultra-capacitor energy storage system to absorb energy at high power associated with a long down-hill decent, for example, is prohibitively expensive.
Gas turbine engines have the additional advantage of being highly fuel flexible and fuel tolerant. For example, gas turbines can be operated on a variety of fuels such as diesel, gasoline, ethanol, methanol, natural gas, biofuels and hydrogen. The performance of gas turbine engines can be improved by making use of electrical energy recovered by a regenerative braking system. These improvements may include extending component lifetimes, pre-heating of fuels and providing an engine braking capability analogous to the Jacobs brake used by piston engines.
There remains a need for compact thermal energy storage devices to better enable gas turbine engines to recover energy from braking so as to improve both engine and braking performance of these engines applied to vehicular propulsion.